The present invention relates generally to a vacuum cleaner, and more particularly to a device for sensing the amount of dust, refuse, etc. flowing into the suction path of a vacuum cleaner so as to automatically adjust the dust suction force.
In a conventional vacuum cleaner, there is provided a device for sensing the amount of dust flowing into a suction path by means of a light emitting element and photoreceptor attached to the inside of the suction path facing each other, whereby the rotating speed of a fan motor is controlled so as to adjust the dust suction force. In this case, since the light emitting element an photoreceptor are exposed to the dust in the suction path, the dust accumulates on them, degrading the performance. In order to offset such performance degradation of the light emitting element and photoreceptor there has been proposed a dust sensing device for an electric cleaner disclosed in EPO Laid-Open Patent Publication No. 347, 223 published on Dec. 20, 1989.
In this publication, the light emitting element and photoreceptor are provided with covers that are attached flush with the inside of the suction path. In addition, there is also provided a surface which is outwardly sloped from the covers towards the inlet of the dust suction so as to increase the speed of the dust flow in the region of the light emitting element and photoreceptor, thus preventing the dust from being attached thereto by dust. In addition, the light radiating end of the light emitting element has a smaller diameter so as to prevent the dispersion of the light and thereby improve dust-sensing capability.
However, in such a dust-sensing device, the diameter of the suction path cannot provide a sloped surface of sufficient height, so that dust attaches to the covers of the light emitting element and photoreceptor thus degrading their sensing capability. Moreover, the light radiating end of the light emitting element is too small to precisely and sufficiently detect the amount of dust flow.